Steering is the act of maintaining or altering the direction in which a vessel is proceeding. This control of a vessel's direction is usually effected by a stern rudder, which, as ordinarily fitted, swings on the vessel's stern-post, and can be set at any required angle with the vessel's fore and aft line. The rudder is turned by what is in effect a lever called the tiller, or helm, which is secured to the rudder-head, and either projects forward from the rudder-head (as is often the case in boats and small vessels) or projects aft from the rudder-head (as in most large vessels). The tiller may in some cases be grasped and turned by hand; but in general a wheel with axle and wheel chains is used to turn the tiller. Where steam-steering gear is fitted it is controlled by a small steering-wheel. When on board a vessel and looking forward—i.e. towards the bow—the right-hand side of the vessel is called the starboard side, and the left hand the port side. The port side was formerly called the larboard side. The order 'port the helm' demands that the after part of the stern rudder should be swung round towards the starboard side of the vessel. Where there is a free tiller projecting forward from the rudder-head this is, of course, accomplished by moving the free end of the tiller towards the port side of the vessel, and this gave rise to the terms of the order. Where a wheel is used the intermediate gearing is usually so fitted that to 'port the helm' the top spoke of the wheel must be pulled down towards the starboard side of the ship. The effect produced in the way of turning the vessel where 'the helm is ported' is as follows: in the case of a sailing-vessel or of other vessels whose propellers are not placed at or near the stern, the hull is turned so that the head of the vessel appears to turn towards its own starboard side when the hull is moving ahead, and towards its own port side when the hull is moving astern; but in the case of vessels whose propelling apparatus works in the water at or near the stern, the first turning effect named is produced when the propeller (and not necessarily the hull) is going ahead, and the second turning effect is produced when the propeller (and not necessarily the hull) is going astern. The effect of the order to 'starboard the helm' is precisely the opposite of all this. The sailors of some foreign nations obey these orders by putting the wheel the opposite way to the above (the British) usage.
The kind of rudder called the 'balanced rudder' has about one-third of its area before the axis about which the rudder rotates. Bow rudders, as well as stern rudders, have been fitted to river-boats, telegraph-laying vessels, ferry-boats, &c., where such vessels are required to run with either end first. In this case one rudder is locked while the other is in use. Two rudders astern have also been recently tried with good effect. In regard to the effect produced upon the steering by the propeller or propellers, the adoption of twin screw-propellers, one on each side of the mid-ship line, has enormously increased the rapidity of steering by working one propeller only, or by simultaneously working one ahead and the other astern. A single screw-propeller has of itself a twisting action on the hull, more especially when the propeller is going astern, the effect being in the latter case to apparently turn the ship's head towards her own starboard side with a right-hand propeller, and towards her own port side with a left-hand propeller. In all these cases, while it is usual to speak of the rudder, propeller, &c. turning the ship's head, it is probable that most of the turning effect is the result of the ship's stern turning the opposite way from the apparent direction in which the ship's head turns. For steering racing and other boats, see ROWING, p. 10. See also BOAT, YACHT, RULE OF THE ROAD.